LIVING SUBSTANCE 19 



mained largely theoretical until more recently, although it is quite 

 true that an expert knowledge of more than one of these fundamental 

 sciences can scarcely be demanded of any physiologist. This new 

 tendency soon forced physiologists to confine their constructive work 

 either to physical or to chemical physiology. The former group of 

 investigators includes such men as E. H. Weber (1795-1878), Volk- 

 mann (1801-1877), Ludwig (1816-1895), Helmholtz (1821-1894), Du 

 Bois-Reymond (1818-1896), Marey (1830-1904), Bernard (1813-1878); 

 and the latter, such men as Voit (1831-1908), Pfiuger (1829-1910), 

 Kossel (1853), Zuntz (1847), and Hofmeister (1808-1878). 



Physiology, therefore, belongs essentially to the nineteenth cen- 

 tury. It is a comparatively new science, but is unfolding itself 

 very rapidly, so that it now forms the chief basis of modern medicine. 

 This is the age of the experimental sciences and very rightly so,because 

 in them lies our greatest hope of benefiting mankind. As Verworn 

 expresses it, the struggle for existence forces man to master the forces 

 of nature and to eradicate all those which tend to enfeeble him. 

 Physiology constitutes a means which is used chiefly to combat the 

 latter. Its ultimate object, therefore, is the welfare of mankind. 

 In order to attain this end, it cannot confine itself to man and the 

 higher animals, but must include living matter wherever found, 

 even that forming the most primitive organisms and plants. For 

 this reason, physiology does not always present a wholly practical 

 aspect, but follows at times a purely scientific course of inquiry. 

 The results of the latter, however, are not to be undervalued, because 

 as man is not accessible to physiological methods, excepting in a few 

 special instances, we are constantly forced to base our conclusions 

 upon the fundamental processes displayed by the lower forms of life. 

 That a direct comparison of this kind is permissible in most cases, 

 has been fully demonstrated experimentally. 



Animate and Inanimate Material. — Since physiology purposes to 

 analyze the phenomena of life, it becomes necessary to familiarize our- 

 selves with the fundamental characteristics of living substance. The 

 layman most generally places the greatest stress upon the production 

 of mechanical energy, such as is evinced by those apparently spon- 

 taneous movements which are made use of by living entities in chang- 

 ing their position in space. As a last means of differentiation between 

 animate and inanimate bodies he employs those activities which are 

 associated with respiration and the action of the heart. A more far- 

 reaching differentiation, however, may be attempted upon the basis 

 of morphological, genetic, physical and chemical peculiarities.^ Thus, 

 it has been said that inorganic bodies possess definite geometric pro- 

 portions, and that they contain no organs and exhibit the simplest 

 possible organization. A brief survey, however, will show that these 

 characteristics are also presented by living substance, because organ- 



1 Verworn, AUgemeine Physiologie, Jena, 1909; and Irritability, Yale Univ. 

 Press, 1913. 



